1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device and a manufacturing method thereof.
The present invention relates to, for example, a transistor, a semiconductor device, and manufacturing methods thereof. The present invention relates to, for example, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, an imaging device, a processor, or an electronic device. The present invention relates to a method for manufacturing a display device, a liquid crystal display device, a light-emitting device, a memory device, or an electronic device. The present invention relates to a driving method of a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a memory device, or an electronic device.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, a light-emitting device, a lighting device, an imaging device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor over a substrate having an insulating surface has attracted attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and a display device. Silicon is known as a semiconductor applicable to a transistor.
As silicon which is used as a semiconductor of a transistor, either amorphous silicon or polycrystalline silicon is used depending on the purpose. For example, in a transistor included in a large display device, it is preferable to use amorphous silicon, which can be used to form a film on a large substrate with the established technique. In a transistor included in a high-performance display device where a driver circuit and a pixel circuit are formed over the same substrate, it is preferred to use polycrystalline silicon, which can form a transistor having high field-effect mobility. As a method for forming polycrystalline silicon, high-temperature heat treatment and laser light treatment which are performed on amorphous silicon have been known.
In recent years, transistors containing oxide semiconductors (typically, In—Ga—Zn oxide) have been actively developed.
Oxide semiconductors have been researched since early times. In 1988, it was disclosed to use a crystal In—Ga—Zn oxide for a semiconductor element (see Patent Document 1). In 1995, a transistor containing an oxide semiconductor was invented, and its electrical characteristics were disclosed (see Patent Document 2).
In 2010, a transistor containing a crystalline In—Ga—Zn oxide that has more excellent electrical characteristics and higher reliability than a transistor containing an amorphous In—Ga—Zn oxide has been developed (see Patent Document 3). The crystalline In—Ga—Zn oxide has c-axis alignment and thus is called a c-axis-aligned crystalline oxide semiconductor (CAAC-OS) or the like.
The transistor containing the CAAC-OS, since its discovery, has been reported to have excellent electrical characteristics. The transistor containing the CAAC-OS has characteristics superior to those of a transistor containing silicon in the following respects, for example.
It has been reported that the transistor containing the CAAC-OS is less likely to be affected by phonon scattering even with a short channel; thus, the field-effect mobility is less likely to be decreased (see Non-Patent Document 1). It has been also reported that a transistor containing the CAAC-OS and having a surrounded channel (s-channel) structure exhibits favorable switching characteristics even with a short channel (see Non-Patent Document 2). The transistor containing the CAAC-OS operates at high speed. For example, Non-Patent Document 3 reports a cutoff frequency of 20 GHz. Furthermore, it has been reported that the transistor containing the CAAC-OS has high breakdown voltage characteristics (see Patent Document 4) and has little variation in characteristics due to temperature (see Patent Document 5).